This invention relates to field emitter technology, and more particularly, to electron emitters and method for forming them.
Cathode ray tube (CRT) displays, such as those commonly used in desk-top computer screens, function as a result of a scanning electron beam from an electron gun, impinging on phosphors on a relatively distant screen. The electrons increase the energy level of the phosphors. The phosphors release energy imparted to them from the bombarding electrons, thereby emitting photons, which photons are transmitted through the glass screen of the display to the viewer.
Flat panel displays have become increasingly important in appliances requiring lightweight portable screens. Currently, such screens use electroluminescent, liquid crystal, or plasma technology. A promising technology is the use of a matrix addressable array of cold cathode emission devices to excite phosphor on a screen.
In U.S. Pat. No. 3,875,442, entitled xe2x80x9cDisplay Panel,xe2x80x9d Wasa et. al. disclose a display panel comprising a transparent gas-tight envelope, two main planar electrodes which are arranged within the gas-tight envelope parallel with each other, and a cathodeluminescent panel. One of the two main electrodes is a cold cathode, and the other is a low potential anode, gate, or grid. The cathode luminescent panel may consist of a transparent glass plate, a transparent electrode formed on the transparent glass plate, and a phosphor layer coated on the transparent electrode. The phosphor layer is made of, for example, zinc oxide which can be excited with low energy electrons.
Spindt, et. al. discuss field emission cathode structures in U.S. Pat. Nos. 3,665,241, and 3,755,704, and 3,812,559, and 4,874,981. To produce the desired field emission, a potential source is provided with its positive terminal connected to the gate, or grid, and its negative terminal connected to the emitter electrode (cathode conductor substrate). The potential source may be made variable for the purpose of controlling the electron emission current. Upon application of a potential between the electrodes, an electric field is established between the emitter tips and the grid, thus causing electrons to be emitted from the cathode tips through the holes in the grid electrode.
An array of points in registry with holes in grids are adaptable to the production of gate emission sources subdivided into areas containing one or more tips from which areas of emission can be drawn separately by the application of the appropriate potentials thereto.
There are several methods by which to form the electron emission tips. Examples of such methods are presented in U.S. Pat. No. 3,970,887 entitled, xe2x80x9cMicro-structure Field Emission Electron Source.xe2x80x9d
The performance of a field emission display is a function of a number of factors, including emitter tip or edge sharpness.
In the process of the present invention, a dopant material which effects the oxidation rate or the etch rate of silicon, is diffused into a silicon substrate or film. xe2x80x9cStalksxe2x80x9d or xe2x80x9cpillarsxe2x80x9d are then etched, and the dopant differential is used to produce a sharpened tip. Alternatively, xe2x80x9cfinsxe2x80x9d or xe2x80x9chedgesxe2x80x9d may be etched, and the dopant differential used to produce a sharpened edge.
One of the advantages of the present invention is the manufacturing control, and available process window for fabricating emitters, particularly if a high aspect ratio is desired. Another advantage of the present invention is its scalability to large areas.